Field sequential liquid crystal display device and driving method thereof, and head mounted display

ABSTRACT

A display with high resolution and reduced flicker of image. The driving method of this invention, or the field sequential driving method, divides one frame of image into a plurality of subframes, i.e., divides the period of one image frame into a plurality of subframe periods; displays red, green and blue images during the corresponding subframe periods; and, when these color images are to be displayed, turns on the corresponding red, green and blue backlights successively to feed light to the display section.

BACKGROUND OF THE INVENTION

(1) Technical Field

The present invention relates to a field sequential liquid crystaldisplay device capable of displaying color images, and the inventionrelates more specifically to an active matrix type liquid crystaldisplay.

(2) Related Art

In recent years the active matrix liquid crystal display is being widelyused for personal computers. It is not only used for the notebook typepersonal computers but also for the desktop personal computers with alarge screen.

The active matrix liquid crystal display used on personal computers arerequired to display a plurality of information at one time and also tohave a capability of full-color display at high definition level andwith high quality.

The conventional active matrix color liquid crystal display forms acolor image by passing white light through red, green and blue colorfilters provided over each of pixels. Hence, in the conventional activematrix color liquid crystal display, the resolution will be reduced toone third of that of the actual active matrix liquid crystal display.For example, an active matrix liquid crystal display having (640×3×480)pixels can only produce an image corresponding to the resolution of VGAstandard, which is (640×480). An active matrix liquid crystal displaywith (800×3×600) pixels can only display an image corresponding to theresolution of SVGA standard, which is (800×600). Hence, to produce animage corresponding to high resolution requires three times the numberof pixels.

To solve the problem described above, a study has been conductedrecently on a method different from the conventional color displaymethod. This driving method, called a field sequential driving method,divides one frame of image into three subframes and turns on red, greenand blue backlights each for one-third frame duration to display animage corresponding to that color for one-third frame duration.

FIG. 22 is a timing chart of the conventional field sequential drivingmethod. The timing chart of the conventional field sequential drivingmethod in FIG. 22 shows a start signal for writing a video signal(V_(sync) signal), turn-on timing signals (R, G and B) for red, greenand blue LEDs, and a video signal (VIDEO). T_(f) represents a frameperiod. T_(R), T_(G) and T_(B) represent durations in which red, greenand blue LEDs are lit, respectively.

A video signal supplied to the liquid crystal panel, for example R₁, isobtained by compressing an original red video signal entered fromoutside to one-third in the time axis direction. A video signal suppliedto the liquid crystal panel, for example G₁, is obtained by compressingan original green video signal entered from outside to one-third in thetime axis direction. A video signal supplied to the liquid crystalpanel, for example B₁, is obtained by compressing an original blue videosignal entered from outside to one-third in the time axis direction.

In the conventional field sequential driving method, the R, G and B LEDsare turned on successively during their corresponding LED turn-onperiods T_(R), T_(G) and T_(B). During the red LED turn-on period(T_(R)), a red video signal (R₁) is supplied to the liquid crystal panelto write one screenful of a red image on the liquid crystal panel.During the green LED turn-on period (T_(G)), a green video signal (G₁)is supplied to the liquid crystal panel to write one screenful of agreen image on the liquid crystal panel. During the blue LED turn-onperiod (T_(B)), a blue video signal (B₁) is supplied to the liquidcrystal panel to write one screenful of a blue image on the liquidcrystal panel. These three screenfuls of image written into forms oneframe.

The color display based on the conventional field sequential drivingmethod has three times the resolution of the conventional color display.With this conventional field sequential driving method, however, becausered, blue and green images are each displayed once for one-third theduration of one frame, the flicker of the screen becomes a very seriousproblem. Because of the flicker, the user cannot stand many hours of useof the display.

The present invention has been accomplished in view of theabove-mentioned drawback and its object is to provide a display capableof minimizing the flicker and having a high resolution.

SUMMARY OF THE INVENTION

The present invention provides a driving method for the field sequentialliquid crystal display, wherein one image frame comprises n (n is aninteger of 2 or more) subframes, the subframes comprise red, green andblue images, and a red, a green or a blue backlight turns oncorresponding to the display of the red, the green or the blue image.

The n may be 3.

The invention further provides a field sequential liquid crystal displaywhich comprises: backlights for feeding red light, green light and bluelight; and a display section for displaying an image when a voltage isapplied to a liquid crystal; wherein the display section displays aplurality of frames in one second, the frame comprises n (n is aninteger of 2 or more) subframes, the subframes comprise a red image, agreen image and a blue image, and the backlights feed red light, greenlight or blue light to the display section when the red image, the greenimage or the blue image is to be displayed.

The n may be 3.

The liquid crystal may be a ferroelectric liquid crystal.

The invention further provides a field sequential liquid crystal displaywhich comprises: backlights having a red LED, a green LED and a blueLED; and a display section for displaying an image when a voltage isapplied to a liquid crystal; wherein the display section displays aplurality of frames in one second, the frame comprises n (n is aninteger of 2 or more) subframes, the subframes comprise a red image, agreen image and a blue image, and the red LED, the green LED or the blueLED feeds light to the display section when the red image, the greenimage or the blue image is to be displayed.

The n may be 3.

The liquid crystal may be a ferroelectric liquid crystal.

The invention further provides a head mounted display (HMD) using thefield sequential liquid crystal display.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the outline configuration of aliquid crystal display using the driving method according to theinvention.

FIG. 2 is a timing chart of signals in the driving method of theinvention.

FIG. 3 is a schematic diagram showing one embodiment of a liquid crystaldisplay using,the driving method of the invention.

FIG. 4 is a block diagram showing the flows of signals in one embodimentof a liquid crystal display using the driving method of the invention.

FIG. 5 is a timing chart of signals in one embodiment of a liquidcrystal display using the driving method of the invention.

FIG. 6 is a schematic diagram showing the outline configuration of oneembodiment of a HMD using the driving method of the invention.

FIG. 7 is a schematic diagram showing the outline configuration of oneembodiment of a HMD using the driving method of the invention.

FIG. 8 is a schematic diagram showing an LED backlight used in oneembodiment of a HMD using the driving method of the invention.

FIG. 9 is a schematic diagram showing the outline configuration of oneembodiment of a HMD using the driving method of the invention.

FIG. 10 is a schematic diagram showing the outline configuration of oneembodiment of a HMD using the driving method of the invention.

FIG. 11 is a schematic diagram showing the outline configuration of oneembodiment of a liquid crystal display using the driving method of theinvention.

FIG. 12 is a schematic diagram showing the outline configuration of oneembodiment of a HMD using the driving method of the invention.

FIG. 13 is a schematic diagram showing the outline configuration of oneembodiment of a HMD using the driving method of the invention.

FIG. 14 is a schematic diagram showing the outline configuration of anLCD panel used in one embodiment of a liquid crystal display using thedriving method of the invention.

FIG. 15 is a schematic diagram showing an example of method ofmanufacturing an LCD panel used in the liquid crystal display using thedriving method of the invention.

FIG. 16 is a schematic diagram showing an example of method ofmanufacturing an LCD panel used in the liquid crystal display using thedriving method of the invention.

FIG. 17 is a schematic diagram showing an example of method ofmanufacturing an LCD panel used in the liquid crystal display using thedriving method of the invention.

FIG. 18 is a schematic diagram showing an example of method ofmanufacturing an LCD panel used in the liquid crystal display using thedriving method of the invention.

FIG. 19 is a schematic diagram showing an example of LCD panel used inthe liquid crystal display using the driving method of the invention.

FIG. 20 is a schematic diagram showing an example of LCD panel used inthe liquid crystal display using the driving method of the invention.

FIG. 21 shows outline views showing examples of semiconductor apparatususing the liquid crystal display using the driving method of theinvention.

FIG. 22 is a timing chart for the conventional field sequential drivingmethod.

FIG. 23 is a graph showing an applied voltage-transmissivitycharacteristic of a thresholdless antiferroelectric mixed liquidcrystal.

FIG. 24 shows outline views showing examples of semiconductor apparatususing the liquid crystal display using the driving method of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The driving method of this invention is a field sequential drivingmethod which divides one frame of an image into a plurality ofsubframes, i.e., divides one frame interval into a plurality of subframeintervals, and displays red, green and blue images in the correspondingsubframe intervals by turning on red, green and blue backlights tosupply the corresponding colors of light to the display section.

The driving method of the invention will be explained by referring toFIG. 1, which shows the outline configuration of a transmission typeliquid crystal display using the driving method of the invention.Designated 101 is an LCD panel (liquid crystal display panel) whichdisplays an image. Denoted 102 is a light conductor plate which makeslight from the LED backlight a plane light source that is uniform inintensity in a plane. Reference number 103 represents an LED backlightwith a plurality of LEDs (light emitting diodes) 104. The LED backlight103 has a plurality of red (R), green (G) and blue (B) LEDs 104. Hence,the LED backlight 103 can be said to be a light source capable ofsupplying red, green and blue light. Denoted 105L and 105R are schematicrepresentations of left and right eyeballs of an observer.

The red, blue or green light from the LED backlight 103 is renderedin-plane uniform light by the light conductor plate 102, which is thenthrown onto the LCD panel 101. The light incident on the LCD panel 101is optically modulated by the LCD panel and given image information.Here a pair of polarizing plates (not shown) with their polarizationaxes crossing at right angles to each other are arranged on both sidesof the LCD panel 101. The light that was given image information by theLCD panel 101 is detected by the eyeballs 105L and 105R of the observerwho now recognizes the image.

A timing chart of the driving method of this invention is shown in FIG.2. The timing chart of FIG. 2 shows a video signal writing start signal(V_(sync) signal), red (R), green (G) and blue (B) LED turn-on timingsignals (R, G and B), and a video signal (VIDEO). T_(f) represents aframe period. T_(sf) represents a subframe period, which is 1/n of theframe period T_(f) (T_(f)=n·T_(sf), n is an integer of 2 or more). Theone subframe period comprises a subframe R period (T_(sfR)), a subframeG period (T_(sfG)) and a subframe B period (T_(sfB)).

The video signal supplied to the liquid crystal panel, for example R₁,is obtained by compressing the original red video signal entered fromoutside (original video-R) by 1/(3n) times in the time axis direction.The video signal supplied to the liquid crystal panel, for example G₁,is obtained by compressing the original green video signal entered fromoutside (original video-G) by 1/(3n) times in the time axis direction.The video signal supplied to the liquid crystal panel, for example B₁,is obtained by compressing the original blue video signal entered fromoutside (original video-B) by 1/(3n) times in the time axis direction.

In the driving method of this invention, the R, G and B LEDs are turnedon during the corresponding subframe R period T_(sfR), subframe G periodT_(sfG), and subframe B period T_(sfB). During the subframe R periodT_(sfR), the red video signal (R₁) is fed to the liquid crystal panel towrite one screenful of a red image (subframe R) on the liquid crystalpanel. During the subframe G period T_(sfG), the green video signal (G₁)is fed to the liquid crystal panel to write one screenful of a greenimage (subframe G) on the liquid crystal panel. During the subframe Bperiod T_(sfB), the blue video signal (B₁) is fed to the liquid crystalpanel to write one screenful of a blue image (subframe B) on the liquidcrystal panel. That is, in the driving method of this invention, thevideo signal (R₁, G₁, B₁) is supplied during each subframe period(T_(sf)) to form one frame by writing a subframe n times.

When the driving method of this invention is used to rewrite 60 framesof image in a second, for example, the frame period is T_(f)=1/60 16.7msec. Hence, the subframe period in this case is T_(sf)≈(16.7/n) msec.Each one-third of the subframe period T_(sf) is the subframe R periodT_(sfR), the subframe G period T_(sfG), and the subframe B periodT_(sfB) and thus T_(sfR)=T_(sfG)=T_(sfB)≈(5.57/n) msec.

Forming one frame of image with a plurality of subframes in this wayrealizes a high-speed rewriting of an image, significantly reducing thescreen flicker experienced with the conventional device.

This invention will be explained in more detail in conjunction with thefollowing embodiments.

Embodiment 1

Let us turn to FIG. 3, which shows the outline configuration of atransmission type liquid crystal display using the driving method ofthis invention. The transmission type liquid crystal display of thisembodiment has a resolution of 640×480 (so-called VGA). Denoted 301 isan LCD panel (liquid crystal panel) for displaying an image. Designated302 is a light conductor plate to make the light from the LED backlight303 in-plane uniform. That is, the light conductor plate 302 and LEDbacklight 303 together form an in-plane light source. The LED backlight303 has a plurality of LEDs 304. The LED backlight has a plurality ofgroups of red (R), green (G) and blue (B) LEDs 304. Reference number305L and 305R represent left and right eyeballs of an observer.

The flow of signals in the transmission type liquid crystal display ofthis embodiment will be explained by referring to a block diagram (FIG.4). In FIG. 4, reference number 401 represents a video signal sourcewhich feeds original image signals for R, G, B (original video-R,original video-G and original video-B) to an A/D converter circuit 402.The original video signal is converted by the A/D converter circuit 402into the original digital sign. Then, these original digital videosignals (original digital video-R, original digital video-G and originaldigital video-R) are supplied to an n-speed field sequential colorsignal generation circuit 403. The value of n is equal to that of n usedfor dividing one frame into n subframes. The n-speed field sequentialcolor signal generation circuit 403 compresses the original videosignals for R, G, B (original video-R, original video-G and originalvideo-B) by 1/(3n) times in the time axis direction. Then, fieldsequential color video signals (R₁, G₁, B₁, R₂, G₂, B₂, . . . )corresponding to the R, G, B and compressed by 1/(3n) times in the timeaxis direction are supplied to an LCD controller 404. At the same time,the n-speed field sequential color signal generation circuit 403generates LED turn-on timing signals (R, G, B) for turning on the LEDsthat are to be supplied to an LED turn-on circuit 405.

The LCD controller 404 supplies the field sequential color video signalssuccessively to the LCD panel 301. The LED turn-on circuit 405successively feeds the LED turn-on timing signals to the LED backlight303.

A block diagram illustrating an outline configuration of the LCD panelis shown in FIG. 14. The LCD panel of this embodiment has a sourcesignal line side driving circuit (A) 301-1, a source signal line sidedriving circuit (B) 301-8, a gate signal line side driving circuit (A)301-9, a gate signal line side driving circuit (B) 301-12, and a pixelmatrix circuit 301-13.

The source signal line side driving circuit (A) 301-1 comprises a shiftregister circuit 301-2, a buffer circuit 301-3, a latch circuit (1)301-4, a latch circuit (2) 301-5, a level shifter circuit 301-6, and aD/A converter circuit 301-7. The source signal line side driving circuit(A) 301-1 supplies a video signal (gray scale voltage signal) to anodd-numbered source signal line.

The operation of the source signal line side driving circuit (A) 301-1will be explained. The shift register circuit 301-2 receives a startpulse and a clock signal. Based on the start pulse and clock signal, theshift register circuit 301-2 feeds the timing signals successively tothe buffer circuit 301-3. The shift register circuit 301-2 comprises aplurality of inverters and a plurality of clocked inverters.

The timing signal from the shift register circuit 301-2 is buffered bythe buffer circuit 301-3. Because many circuits or elements areconnected to the circuits ranging from the shift register circuit 301-2to the source signal line connected to the pixel matrix circuit 301-13,these circuits have a large load capacitance. To prevent the timingsignals from becoming “dull” due to the large load capacitance, thebuffer circuit 301-3 is provided.

The timing signals buffered by the buffer circuit 301-3 are fed to thelatch circuit (1) 301-4, which, when it receives the timing signals,successively takes in the digital video signal (R₁, G₁, B₁, R₂, G₂, B₂,. . . ) fed from the LCD controller and retains them.

The period of time during which the digital video signals are completelywritten into all latch circuits of the latch circuit (1) 301-4 is calledone line period. That is, the time duration from the point of time atwhich the digital video signal starts to be written into the leftmostlatch circuit of the latch circuit (1) 301-4 to the point of time atwhich the digital video signal is completely written into the rightmostlatch circuit is one line period.

After the writing of the digital video signals into the latch circuit(1) 301-4 has finished, the digital video signals written into the latchcircuit (1) 301-4 are sent to and written into the latch circuit (2)301-5 at one time when a latch pulse flows through a latch pulse lineconnected to the latch circuit (2) 301-5 in synchronism with theoperation timing of the shift register circuit 301-2.

The latch circuit (2) 301-5 that has sent out the digital video signalsto the latch circuit (2) 301-5 is successively written again withdigital video signals that are fed from the LCD controller 404 by thetiming signal from the shift register circuit 301-2.

During the second 1-line period, the digital video signals sent to thelatch circuit (2) 301-5 is supplied to the level shifter circuit 301-6in synchronism with the start of the second 1-line period. The levelshifter circuit 301-6 raises the voltage levels of the digital videosignals which are then sent to the D/A converter circuit 301-7. The D/Aconverter circuit 301-7 converts the digital video signals into analogsignals (gray scale voltages) and feeds them to the corresponding sourcesignal lines. The analog signals supplied to the source signal lines aresupplied to the pixel TFT's source regions of the pixel matrix circuitconnected to the source signal lines.

In the gate signal line side driving circuit (A) 301-9, timing signalsfrom the shift register 301-10 are fed to a buffer circuit 301-11 andthen to the corresponding gate signal lines (scan lines). The gatesignal lines are each connected with pixel TFT's gate electrodes for oneline. Because all the pixel TFTs for one line must be turned onsimultaneously, the buffer circuit 301-11 used has a largecurrent-carrying capacity.

The scan signals from the gate signal line side shift register switchthe corresponding pixel TFTs, and the analog signals (gray scalevoltages) from the source signal line side driving circuit are suppliedto the pixel TFTs to driving the liquid crystal molecules.

Denoted 301-8 is a source signal line side driving circuit (B) with thesame configuration as that of the source signal line side drivingcircuit (A) 301-1. The source signal line side driving circuit (B) 301-8feeds video signals to even-numbered source signal lines.

Designated 301-12 is a gate signal line side driving circuit (B) withthe same configuration as that of the gate signal line side drivingcircuit (A) 301-9.

FIG. 5 shows a timing chart for the driving method of this embodimentwith n=3. The timing chart of FIG. 5 shows a start signal of writingvideo signal (V_(sync) signal), red (R), green (G) and blue (B) LEDturn-on timing signals (R, G and B), and a video signals (VIDEO). T_(f)represents a frame period. T_(sf) represents a subframe period which is⅓ of the frame period T_(f) (T_(f)=3 T_(sf)).

The video signal fed to the LCD panel, for example R₁, is obtained bycompressing the original red video signal entered from outside (originalvideo-R) by 1/(3×3)={fraction (1/9)} times in the time axis direction.The video signal fed to the LCD panel, for example G₁, is obtained bycompressing the original green video signal entered from outside(original video-G) by {fraction (1/9)} times in the time axis direction.The video signal fed to the LCD panel, for example B₁, is obtained bycompressing the original blue video signal entered from outside(original video-B) by {fraction (1/9)} times in the time axis direction.

In the driving method of this embodiment (n=3), the R, G and B LEDs areturned on during the subframe R period (T_(sfR)), subframe G period(T_(sfG)) and subframe B period (T_(sfB)), respectively. During thesubframe R period s the red digital video signal (R₁) is supplied to theliquid crystal panel to write one screenful of a red image (subframe R)on the liquid crystal panel. During the subframe G period T_(sfG) thegreen digital video signal (G₁) is supplied to the liquid crystal panelto write one screenful of a green image (subframe G) on the liquidcrystal panel. During the subframe B period T_(sfB) the blue digitalvideo signal (B₁) is supplied to the liquid crystal panel to write onescreenful of a blue image (subframe B) on the liquid crystal panel. Thatis, in the driving method of the invention, the digital video signals(R₁, G₁, B₁) are supplied during each subframe period T_(sf) and oneframe is formed from three subframes.

When the image is rewritten at the rate of, for example, 60 frames persecond, the subframe period is T_(sf)=1/60/3≈5.56 msec. Each one-thirdof this subframe period T_(sf) is the subframe R period T_(sfR), thesubframe G period T_(sfG), and the subframe B period T_(sfB) and thusT_(sfR)=T_(sfG)=T_(sfB)≈1.85 msec.

Now, the operation of writing the digital video signal during thesubframe R period T_(sfR)=1.85 msec will be explained. The transmissiontype liquid crystal display of this embodiment has a resolution of640×480 and the source signal side driving circuit is capable ofline-sequential driving of source signals. The liquid crystal materialused in the transmission type liquid crystal display of this embodimentis a ferroelectric liquid crystal (with a response speed of 38 μsec),which is mixed with a photocurable liquid crystal acrylate monomer,injected into the transmission type liquid crystal display and thenirradiated with ultraviolet rays. Hence the liquid crystal materialexhibits a monostable characteristic.

The driving circuit used in this embodiment writes video datacorresponding to a red image into 640 pixel TFTs for one line in about 2μsec. Thus, the time taken for completely writing all pixels making upone subframe R is 2 μsec×480=960 μsec=0.96 msec. Because the responsetime of the liquid crystal is 38 μsec, the time taken by the liquidcrystal of the 480th line to respond is 0.998 msec from the point intime at which the pixels of the first line have begun to be written.Therefore, in the subframe R period T_(sfR), the image writing into allthe corresponding pixels is finished in the first 1.26 msec and, in theremaining 50 msec or so, the red LED turns on, allowing the image on theLCD panel to be recognized by an observer.

Likewise, during the next subframe G period T_(sfG), the datacorresponding to a green image is written into 640 pixel TFTs for oneline in about 2 μsec. In the subframe G period T_(sfG), the imagewriting into all the corresponding pixels is finished in the first 1.26msec and, in the remaining 50 msec or so, the green LED turns on,allowing the image on the LCD panel to be recognized by an observer.

Likewise, during the next subframe B period T_(sfB), the datacorresponding to a blue image is written into 640 pixel TFTs for oneline in about 2 μsec. In the subframe B period T_(sfB), the imagewriting into all the corresponding pixels is finished in the first 1.26msec and, in the remaining 50 msec or so, the blue LED turns on,allowing the image on the LCD panel to be recognized by an observer.

The subframe R period T_(sfR), the subframe G period T_(sfG) and thesubframe B period T_(sfB) comprise one subframe period T_(sf). In thisembodiment, this subframe period T_(sf) is repeated three times in thesame way.

By forming one frame of image with a plurality of subframes, ahigh-speed rewriting of image can be realized, thereby substantiallyreducing the flicker of image which was conventionally a problem.

Although we have described an example case of n=3, i.e., n-speed fieldsequential driving, the driving circuit of this invention can also beapplied to other than n=3. It should be noted, however, how many speedsthe field sequential driving will have depends on the response speed ofthe liquid crystal material used in the LCD panel and on the performanceof the driving circuit.

While this embodiment employs an LCD panel that has a digital drivingrcapable of handling digital video signals, it is also possible toconvert the digital video signals into analog signals by the LCDcontroller and supply them to the LCD panel having an analog driver.

The driving method of this invention will be explained in more detail inconjunction with the following embodiments. However, the driving methodof this invention is not limited to the following embodiments.

Embodiment 2

In this embodiment we will explain about the head mounted display(HMD)using the driving method of this invention by referring to FIGS. 6 and7. FIG. 6 shows the outline configuration of the HMD of this embodiment.Reference number 601 represents a HMD body; 602-R and 602-L are LCDpanels; 603-R and 603-L are light conductor plates; and 604-R and 604-Lare LED backlights. In FIG. 7, 605 and 606 are LEDs; and 607-L and 607-Rare eyeballs of an observer. The LCD panel 602-R offers an image for theright eye and the LCD panel 602-L offers an image for the left eye.Hence, the LCD panel 602-R and the LCD panel 602-L may offer the sameimage. It is also possible to provide different images on the LCD panel602-R and on the LCD panel 602-L so that the observer can recognize athree-dimensional image.

The HMD of this embodiment is supplied video signals from the externalvideo signal source (not shown). The HMD of this embodiment has aconstruction as shown in FIG. 4. In this embodiment, the A/D convertercircuit, the n-speed field sequential color signal generation circuit,the LCD controller and the LED turn-on circuit (none of them shown inFIG. 6) are all integrated on a single IC chip (not shown). The A/Dconverter circuit, the n-speed field sequential color signal generationcircuit, the LCD controller and the LED turn-on circuit may be formedintegral with the LCD.

FIG. 8 shows the structures of the LED backlights 609-L and 609-R of theHMD of this embodiment. FIG. 8A shows the striped arrangement of theLED(R) (red LED), the LED(G) (green LED) and the LED(B) (blue LED) thattogether form the LED backlights 609-L and 609-R. This embodimentemploys the LED arrangement as shown in FIG. 8A.

The LEDs making up the LED backlights 609-L and 609-R may be so arrangedthat the three LED colors are staggered from one row to another as shownin FIG. 8B. Further, as shown in FIG. 8C, the LEDs may be arrangeddensely so that as many LEDs as possible can be arranged in thebacklights.

Embodiment 3

Another HMD using the driving circuit of the invention will be explainedin this embodiment by referring to FIGS. 9 and 10. FIG. 9 shows theoutline structure of the HMD of this embodiment. Designated 901 is a HMDbody; 902-R and 902-L are LCD panels; 903-R and 903-L are lightconductor plates; 904-R and 904-L are LED backlights; and 905-R and905-L are mirrors. 906-R and 906-L, though not shown in FIG. 9, areincorporated in the HMD 901. In FIG. 10, 906-R and 906-L are lenses and907-L and 907-R are eyeballs of an observer.

In the HMD of this embodiment, the light from the LED backlights 904-Rand 904-L is formed into plane-like geometries by the light conductorplates 903-R and 903-L and then thrown onto the LCD panels 902-R and902-L. The light incident on the LCD panels 902-R and 902-L is opticallymodulated by the LCD panels 902-R and 902-L and thereby given imageinformation. In this embodiment, too, a pair of polarizing plates (notshown) with their polarization axes crossing at right angles to eachother are arranged on both sides of the LCD panels 902-R and 902-L. Thelight that was given image information by the LCD panels 902-R and 902-Lis bent by mirrors 905-R and 905L, magnified by lenses 906-R and 906-Land then detected by the eyeballs 907-L and 907-R of an observer. TheLCD panel 902-R and the LCD panel 902-L may offer the same image. It isalso possible to provide different images on the LCD panel 902-R and onthe LCD panel 902-L so that the observer can recognize athree-dimensional image.

The HMD of this embodiment is supplied video signals from the externalvideo signal source (not shown). The HMD of this embodiment has aconstruction as shown in FIG. 4. In this embodiment, the A/D convertercircuit, the n-speed field sequential color signal generation circuit,the LCD controller and the LED turn-on circuit (none of them shown inFIGS. 9 and 10) are all integrated on a single IC chip (not shown). TheA/D converter circuit, the n-speed field sequential color signalgeneration circuit, the LCD controller and the LED turn-on circuit maybe formed integral with the LCD.

Embodiment 4

Let us turn to FIG. 11. This embodiment differs from the precedingembodiments in the construction of the LED backlight. The liquid crystaldisplay of this embodiment has an LCD panel 1101 and an LED backlight1102. The LED backlight 1102 has a light conductor plate 1103 and an LED1104. The LED 1104 throws light from the side of the LED backlight. Thelight is then formed into planar light that is then shone onto the LCDpanel 1101. Denoted 1105-L and 1105-R are left and right eyeballs of anobserver.

Embodiment 5

In this embodiment we will explain about a HMD using an LED backlightdescribed in the preceding embodiment 4 by referring to FIGS. 12 and 13.Reference number 1201 represents a HMD body; 1202-R and 1202-L are LCDpanels; and 1203-R and 1203-L are LED backlights. The LED backlights1203-R and 1203-L each have a conductor plate 1204-R, 1204-L and an LED1205-R, 1205-L. 1206-L and 1206-R are left and right eyeballs of anobserver.

Embodiment 6

The method of manufacturing the LCD panel used in the precedingembodiments 1-5 will be explained. In this embodiment, FIGS. 15-18 showan example case of forming a plurality of TFTs on a substrate having aninsulating surface and fabricating a pixel matrix circuit, a drivingcircuit, a logic circuit, etc. in a monolithic structure. Thisembodiment shows how one of pixels in the pixel matrix circuit and aCMOS circuit, a basic circuit of other circuits (driving circuit, logiccircuit, etc.) are formed simultaneously. It is also possible to formthe A/D converter circuit, the n-speed field sequential color signalgeneration circuit, the LCD controller and the LED turn-on circuitintegrally with the LCD. While this embodiment describes a fabricationprocess in a case where the P-channel TFT and N-channel TFT in the CMOScircuit each have a gate electrode, it is also possible to fabricate aCMOS circuit which comprises TFTs having a plurality of gate electrodes,such as double gate type and triple gate type. Further, although thisembodiment employs double gate N-channel TFTs for the pixel TFTs, it ispossible to use single gate or triple gate TFTs.

See FIG. 15A. First, a quartz substrate 1501 as a substrate with aninsulating surface is prepared. Instead of the quartz substrate, asilicon substrate formed with a thermal oxide film may be used. Anamorphous silicon film may also be formed temporarily over the quartzsubstrate and completely thermally oxidized to form an insulating film.It is also possible to use a quartz substrate, a ceramic substrate or asilicon substrate formed with a silicon nitride film as an insulatingfilm. Next, a base film 1502 is formed. In this embodiment, a siliconoxide (SiO₂) 200 nm thick was used as the base film 1502. Then, anamorphous silicon film 1503 is formed. The amorphous silicon film 1503is adjusted so that its final thickness (considering a reduction inthickness after thermal oxidation) will be 10-75 nm (preferably 15-45nm).

In forming the amorphous silicon film 1503 it is important to performstrict control on impurity concentration in the film. In this embodimentthe impurity concentration in the amorphous silicon film 1503 iscontrolled so that the concentrations of C (carbon) and N (nitrogen),impurities that hinder crystallization occurring at a later stage, willboth be less than 5×10¹⁸ atoms/cm³ (typically 5×10¹⁷ atoms/cm³ or less,preferably 2×10¹⁷ atoms/cm³ or less) and that the concentration of O(oxygen) will be less than 1.5×10¹⁹ atoms/cm³ (typically 1×10¹⁸atoms/cm³ or less, preferably 5×10¹⁷ atoms/cm³ or less). If theseimpurities exist in concentrations higher than those shown above, thecrystallization at a later stage will be adversely affected, degradingthe quality of film after crystallization. In this specification, theconcentrations of the above impurity elements are defined by the minimumvalues of the measurements by SIMS (secondary ion mass spectrometry).

To obtain the above construction, it is preferred that the low pressurethermal CVD furnace used in this embodiment be dry-cleaned periodicallyto keep the deposition chamber clean. The dry cleaning may be done bysupplying 100-300 sccm of chlorine fluoride (ClF₃) into the furnaceheated to around 200-400° C. to clean the deposition chamber withfluorine generated by thermal decomposition.

According to the findings of this applicant, with the in-furnacetemperature set at 300° C. and the ClF₃ gas flow set at 300 sccm, it ispossible to completely remove adhering substances (mainly comprised ofsilicon) about 2 μm thick in four hours.

The concentration of hydrogen in the amorphous silicon film 1503 is alsoa very important parameter and it seems that a smaller hydrogen contentwill produce a film with better crystallinity. Thus, the formation ofthe amorphous silicon film 1503 should preferably be done by the lowpressure thermal CVD method. A plasma CVD method can also be used byoptimizing the deposition conditions.

Next, the process of crystallizing the amorphous silicon film 1503 isperformed by using a technology disclosed in JP-A-7-130652 as acrystallization means. Whichever means in the Patent Publication,embodiment 1 or embodiment 2, may be employed. In this embodiment thetechnology described in the embodiment 2 of the PatentPublication(detailed in JP-A-8-78329) is preferably used.

The technology described in JP-A-8-78329 first forms a mask insulatingfilm 1504, used to select catalytic element addition regions, to athickness of 150 nm. The mask insulating film 1504 has a plurality ofopenings through which to add catalytic elements. The locations ofcrystallization regions can be determined by the locations of theopenings (FIG. 15B).

Then, a solution (nickel acetate ethanol solution) 1505 containingnickel (Ni) as a catalytic element for promoting crystallization of theamorphous silicon film 1503 is spin-coated over the film. Other possiblecatalytic elements include cobalt (Co), iron (Fe), palladium (Pd),germanium (Ge), platinum (Pt), copper (Cu) and gold (Au) (FIG. 15B).

The catalytic element addition process described above may use an ionimplantation or plasma doping method using a resist mask. In this case,because reduction in the area of the catalytic element addition regionsand the control of a growth distance in the horizontal growth region arefacilitated, this technology is effective in fabricating miniaturizedcircuits.

After the catalytic element addition process is finished, the substrateis heated at 450° C. for about an hour to remove hydrogen and is thenheat-treated at 500-960° C. (typically 550-650° C.) in the presence ofan inert gas, hydrogen or oxygen for 4-24 hours to crystallize theamorphous silicon film 1503. In this embodiment, the heat treatment isperformed in the presence of nitrogen at 570° C. for 14 hours.

In this process, the crystallization of the amorphous silicon film 1503proceeds preferentially at nuclei generated in the nickel-added regions1506 to form crystal regions 1507 which are made of a polycrystallinesilicon film that has grown almost parallel to the surface of thesubstrate 1501. This crystal region 1507 is called a horizontal growthregion. The horizontal growth region has individual crystals aggregatedin relatively aligned state and thus has an advantage of excellentoverall crystallinity.

Rather than using the mask insulating film 1504, it is possible to applythe nickel acetate solution to the surface of the amorphous siliconfilm.

Referring to FIG. 15D, the next process to be performed is the getteringof the catalytic elements. First, phosphorus ions are selectively doped.With the mask insulating film 1504 formed, phosphorus is doped.Phosphorus is only doped into areas 1508 not covered with thepolysilicon mask insulating film 1504 (these areas are calledphosphorus-added regions 1508). At this time, the dopant accelerationvoltage and the thickness of the mask made of oxide film are optimizedso that phosphorus will not pierce through the mask insulating film1504. The mask insulating film 1504 is not necessarily an oxide film,but the oxide film is advantageous as it does not cause contaminationeven when it contacts an active layer.

The dose of phosphorus is preferably in the range of 1×10¹⁴ to 1×10¹⁵ions/cm². In this embodiment, a dose of 5×10¹⁴ ions/cm² is doped byusing an ion doping apparatus.

The dopant acceleration voltage selected was 10 keV, at which levelphosphorus can hardly pass through the mask insulating film with athickness of 150 nm.

In FIG. 15E, the substrate is annealed in the presence of nitrogen at600° C. for 1-12 hours (in this embodiment, 12 hours) to perform thegettering of nickel element. This causes nickel atoms to be attracted tophosphorus as shown by the arrow in FIG. 15E. At the temperature of 600°C., while phosphorus atoms hardly move in the film, nickel atoms canmove a distance of several hundred μm or more. This shows thatphosphorus is one of the most suited elements for gettering.

Next, by referring to FIG. 16A, the process of patterning a polysiliconfilm will be explained. In this process, steps are taken to ensure thatthe phosphor-added regions 1508, where nickel atoms were gettered, donot remain. In this way, active layers 1509-1511 of a polysilicon filmthat hardly contain nickel element were obtained. The active layer ofpolysilicon films 1509-1511 thus obtained will at later stage form a TFTactive layer.

In FIG. 16B, after the active layers 1509-1511 are formed, a gateinsulating film 1512 comprising silicon is formed over the active layersto a thickness of 70 nm. Then, in the presence of an oxidizingatmosphere the substrate is heat-treated at 800-1100° C. (preferably950-1050° C.) to thermally oxidize an interface between the activelayers 1509-1511 and the gate insulating film 1512.

The heat treatment for the gettering of the catalytic element (catalyticelement gettering process) may be performed at this stage. In that case,the heat treatment is done by using a processing gas containing, ahalogen element to utilize the catalytic element gettering effect by thehalogen element. To produce a sufficient gettering effect by the halogenelement, it is preferred that the heat treatment be performed attemperatures in excess of 700° C. Below this temperature thedecomposition of halides in the processing gas becomes difficult,raising the possibility of a failure to produce the gettering effect.Among the gases containing halogen elements are typically one or morekinds chosen from halogen containing compounds such as HCl, HF, NF₃,HBr, Cl₂, ClF₃, BCl₂, F₂, and Br₂. During this process, when HCl is usedfor example, nickel in the active layer is gettered by the action ofchlorine and is considered to be removed and released as a volatilenickel chloride into the air. When the catalytic elements are to begettered by halogen elements, the catalytic element gettering processmay be performed after the mask insulating film 1504 is removed andbefore the active layer is patterned. The catalytic element getteringprocess may be performed after the active layer has been patterned.Either of these gettering processes may be combined.

Next, a metal film made mainly of aluminum, not shown, is deposited andpatterned to form a prototype of the gate electrode described later. Inthis embodiment, an aluminum film containing 2 wt % of scandium is used.

The gate electrode may also be formed of a polysilicon film doped withan impurity to give the film a certain type of conductivity.

Next, porous anodic oxide films 1513-1520, non-porous anodic oxide films1521-1524 and gate electrodes 1525-1528 are formed by the technologydescribed in JP-A-7-135318 (FIG. 16B).

When the state of FIG. 16B is obtained, the gate insulating film 1512 isetched with the gate electrodes 1525-1528 and porous anodic oxide films1513-1520 as masks. Then, the porous anodic oxide film 1513-1520 areremoved to produce the state of FIG. 16C. In FIG. 16C, shown at1529-1531 are gate insulating films after being processed.

Next, in FIG. 17A, a process of adding an impurity element to give onetype of conductivity is performed. The impurity element used is P(phosphorus) or As (arsenic) for N-channel type and B (boron) or Ga(gallium) for P-channel type.

In this embodiment, the addition of impurities to form N-channel orP-channel TFTs is performed in two processes.

First, an impurity is doped to form N-channel TFTs. The first impurityaddition (in this embodiment, phosphorus (P) is used) is done at a highacceleration voltage of about 80 keV to form n⁻ regions. The ion dopingis adjusted so that the P ion concentration in the n⁻ regions will be1×10¹⁸ atoms/cm³ to 1×10¹⁹ atoms/cm³.

The second impurity doping is done at a low acceleration voltage ofabout 10 keV to form n⁺ regions. Because the acceleration voltage is lowthis time, the gate insulation film works as a mask. The ion doping isadjusted so that the n⁺ regions will have a sheet resistance of 500 Ω orless (preferably 300 Ω or less).

With these processes finished, N-channel TFT source and drain regions1532 and 1533, a low concentration impurity region 1536 and a channelformation region 1539, all constituting a CMOS circuit, are formed.Further, N-channel TFT source and drain regions 1534 and 1535, a lowconcentration impurity region 1537 and channel formation regions 1540and 1514, all constituting the pixel TFT, are also formed (FIG. 17A).

In the state shown in FIG. 17A, the active layer of the P-channel TFTthat forms the CMOS circuit has the same structure as the active layerof the N-channel TFT.

Then, as shown in FIG. 17B, with the N-channel TFTs covered with aresist mask 1542, an impurity ion for giving P type conductivity (inthis embodiment, boron) is doped.

This process is performed in two steps as in the preceding impuritydoping process. Because the N-channel type must be inverted to theP-channel type, the boron (B) ion in a concentration a few times higherthan that of the P ion used in the preceding process is doped.

In this way, P-channel TFT's source and drain regions 1543 and 1544, alow concentration impurity region 1545, and a channel formation region1546, all making up the CMOS circuit, are formed (FIG. 17B).

When a polysilicon film doped with an impurity to give it a certain typeof conductivity is used to form a gate electrode, the low concentrationimpurity regions may be formed by using the known sidewall structure.

Next, impurity ions are activated by a combination of furnace anneal,laser anneal, lamp anneal, etc. At the same time, damages to the activelayer sustained during the impurity doping process are repaired.

Next, in FIG. 17C, a laminated layer consisting of a silicon oxide filmand a silicon nitride film is formed as a first interlayer insulatingfilm 1547, which is then formed with contact holes and source and drainelectrodes 1548-1552 are formed. The first interlayer insulating film1547 may use an organic resin film.

Next, in FIG. 18, a second interlayer insulating film 1553 made oforganic resin film is formed to a thickness of 0.5-3 μm. Among thepossible organic resin films are polyimide, acrylics and polyimideamide.The advantages of the organic resin film include the ease with which thefilm is formed, ease with which the film thickness can be increased, alow parasitic capacitance achieved by a low relative dielectricconstant, and an excellent flatness. An organic resin film other thanthose listed above may also be used.

Next, a part of the second interlayer insulating film 1553 is etchedaway. Over the drain electrode 1552 of the pixel TFT a black matrix 1554is formed with the second interlayer insulating film interposed. Thisembodiment used titanium (Ti) for the black matrix 1554. In thisembodiment, an auxiliary capacitance is formed between the pixel TFT andthe black mask.

Next, a contact hole is formed in the second interlayer insulating film1553 and a pixel electrode 1556 is formed to a thickness of 120 nm.Because this embodiment is a transmission type active matrix liquidcrystal display, a transparent conductive film such as ITO is used as aconductive film forming the pixel electrode 1556.

Then, the entire substrate is heated in the presence of hydrogen at 350°C. for 1-2 hours to hydrogenate the entire element to make up for thedangling bonds in the film (particularly in the active layer). With theabove processes finished, an active matrix substrate having the CMOScircuit and the pixel matrix circuit on the same substrate is completed.

Next, the process of fabricating an active matrix liquid crystal displayusing the active matrix substrate manufactured in the above process willbe described.

An alignment layer 1557 is formed over the active matrix substrate ofFIG. 18B. This embodiment used polyimide for the alignment layer 1557.Then, a counter substrate is prepared. The counter substrate consists ofa glass substrate 1558, a counter electrode 1559 made of a transparentconductive film, and an alignment layer 1560.

This embodiment used a polyimide film for the alignment layer. Thealignment layer, after being formed, is subjected to a rubbingprocessing.

After these steps, the active matrix substrate and the counter substrateare bonded together by a known cell forming process using sealingmaterial and spacers (none of them shown). Then, a ferroelectric liquidcrystal 1561 mixed with a few percent of photocurable liquid crystalacrylate monomer is injected between these substrates and completelysealed with a sealant (not shown). Ultraviolet light was radiated whileapplying voltage to the liquid crystal to photopolymerize the liquidcrystal acrylate monomer.

This completes a transmission type liquid crystal display as shown inFIG. 18C.

Instead of using the amorphous silicon film crystallization methoddescribed in this embodiment, it is possible to crystallize theamorphous silicon film by a laser beam (typically excimer laser beam).

Embodiment 7

This embodiment describes a liquid crystal display using inverse staggertype TFTs as the liquid crystal display capable of realizing the drivingmethod of this invention.

FIG. 19 shows a cross section of an inverse stagger type N-channel TFTthat forms the liquid crystal display of this embodiment. Although onlyone N-channel TFT is shown in FIG. 19, it is needless to say that theCMOS circuit can also be formed by using a P-channel TFT and anN-channel TFT, as in the case of the embodiment 6.

Denoted 1901 is a substrate like the one used in the embodiment 6.Designated 1902 is a silicon oxide film. Reference number 1903represents a gate electrode; 1904 is a gate insulating film; and 1905,1906, 1907 and 1908 are active layers of polysilicon film. Inmanufacturing these active layers, a method similar to the amorphoussilicon film polycrystallization method explained in the embodiment 6was used. It is also possible to crystallize the amorphous silicon filmby a laser beam (preferably a linear laser beam or planar laser beam).Designated 1905 is a source region, 1906 is a drain region, 1907 is alow concentration impurity region (LDD region), and 1908 is a channelformation region. Reference number 1909 denotes a channel protectivefilm, 1910 is an interlayer insulating film, and 1911 and 1912 are asource electrode and a drain electrode, respectively.

Embodiment 8

This embodiment describes a liquid crystal display comprising inversestagger type TFTs whose configuration is different from that of theembodiment 7.

FIG. 20 shows a cross section of an inverse stagger type N-channel TFTthat forms the liquid crystal display of this embodiment. Although onlyone N-channel TFT is shown here, too, it is needless to say that theCMOS circuit can also be formed by using a P-channel TFT and anN-channel TFT, as in the case of the embodiment 6. It should also benoted that the pixel TFT, too, can be formed in the similarconstruction.

Denoted 2001 is a substrate like the one used in the embodiment 6.Designated 2002 is a silicon oxide film. Reference number 2003represents a gate electrode and 2004 is a benzocyclobutane (BCB) filmwhose upper surface is planarized. 2005 is a silicon nitride film. TheBCB film and the silicon nitride film together form the gate insulatingfilm. 2006, 2007, 2008 and 2009 represent active layers of polysiliconfilm. In manufacturing these active layers, a method similar to theamorphous silicon film polycrystallization method explained in theembodiment 1 was used. It is also possible to crystallize the amorphoussilicon film by a laser beam (preferably a linear laser beam or planarlaser beam). Designated 2006 is a source region, 2007 is a drain region,2008 is a low concentration impurity region (LDD region), and 2009 is achannel formation region. 2010 is a channel protective film, 2011 aninterlayer insulating film, and 2012 and 2013 are a source electrode anda drain electrode, respectively.

With this embodiment, because the gate insulating film comprising theBCB film and the silicon nitride film is planarized, the amorphoussilicon film formed over the gate insulating film is also planar. Hence,in polycrystallizing the amorphous silicon film, it is possible toproduce a polysilicon film more uniform than the conventional inversestagger type TFT.

Embodiment 9

While the preceding embodiments concern the liquid crystal display usinga ferroelectric liquid crystal, it is also possible to use a nematicliquid crystal.

Embodiment 10

The field sequential liquid crystal display using the driving circuit ofthis invention has a wide range of applications. This embodimentdescribes semiconductor apparatus incorporating the field sequentialliquid crystal display using the driving circuit of the invention.

Such semiconductor apparatus include video cameras, still cameras,projectors, HMDs, car navigation equipment, personal computers, andportable information terminals (such as mobile computers and cellularphones). An example of these apparatus is shown in FIGS. 21 and 24.

FIG. 21A shows a cellular phone, which comprises a body 2101, a voiceoutput unit 2102, a voice input unit 2103, a field sequential liquidcrystal display 2104, an operation switch 2105, and an antenna 2106.

FIG. 21B shows a video camera, which comprises a body 2107, a fieldsequential liquid crystal display 2108, a voice input unit 2109, anoperation switch 2110, a battery 2111, and an image receiving unit 2112.

FIG. 21C shows a mobile computer, which comprises a body 2113, a cameraunit 2114, an image receiving unit 2115, an operation switch 2116, and afield sequential liquid crystal display 2117.

FIG. 21D shows a HMD for one eye, which comprises a field sequentialliquid crystal display 2118 and a band 2119.

FIG. 24A shows a personal computer, which comprises a body 2001, animage input unit 2002, a field sequential liquid crystal display 2003,and a keyboard 2004.

FIG. 24B shows a goggle type display, which comprises a body 2301, afield sequential liquid crystal display 2302, and arms 2303.

FIG. 24C shows a player using a recording medium recorded with aprogram(hereafter referred to as recording medium), which comprises abody 2401, a field sequential liquid crystal display 2402, a speakerunit 2403, a recording medium 2404 and an operation switch 2405.

FIG. 24D shows a digital camera, which comprises a body 2501, a fieldsequential liquid crystal display 2502, an eyepiece 2503, an operationswitch 2504, and an image receiver (not shown).

Embodiment 11

The field sequential liquid crystal display of the invention can useliquid crystals other than the ferroelectric liquid crystal describedabove. They include the liquid crystals described, for example, in“1998, SID, ‘Characteristics and Driving Scheme of Polymer-StabilizedMonostable FLCD Exhibiting Fast Response Time and High Contrast Ratiowith Gray-Scale Capability’ by H. Furue et al.”; in “1997, SID DIGEST,841, ‘A Full-Color Thresholdless Antiferroelectric LCD Exhibiting WideViewing Angle with Fast Response Time’ by T. Yoshida et al.”; in “1996,J. Mater. Chem. 6(4), 671-673, ‘Thresholdless antiferroelectricity inliquid crystals and its application to displays’ by S. Inui et al.”; andin U.S. Pat. No. 5,594,569.

FIG. 23(A) shows the electrooptical characteristic of monostableferroelectric liquid crystal (FLC) in which FLC that exhibits isotropicphase—cholesteric phase—chiral smectic C phase transition is used tocause transition from cholesteric phase to chiral smectic C phase byapplying DC voltage, and the corn edge is substantially coincided withthe rubbing axis. The display mode by FLC as shown in FIG. 23(A) iscalled “half V-shaped switching mode.” The axis of ordinates in FIG.23(A) represents transmittivity (arbitrary unit) and abcissas appliedvoltage. Regareding “half V-shaped switching mode”, details are taughtin references “Half V-shaped swithcing mode FLCD”, Terada et al.,Proceedings of 46th Spring Meetings of The Society for Applied Physicsof Japan, p1316, March 1999, and “Time Divided Full Color LCD by FLC”,Yoshthara, EKISHO 3(3), 1999, p190.

As shown in FIG. 23(A), low voltage driving and gray scale display ispossible by using such mixed ferroelectric liquid crystals. FLCexhibiting such electrooptical characteristic can be used to the liquidcrystal display of the present invention.

A liquid crystal that exhibits an antiferroelectricity in a certaintemperature range is called an antiferroelectric liquid crystal. Amongmixed liquid crystals having an antiferroelectric liquid crystal, thereare thresholdless antiferroelectric mixed liquid crystals that exhibitan electrooptic response characteristic in which the transmissivitycontinuously changes with respect to an electric field. Somethresholdless antiferroelectric mixed liquid crystals exhibit a V-shapedelectrooptic response characteristic. Some of these thresholdlessantiferroelectric mixed liquid crystals have been found to have drivingvoltages of about ±2.5 V (cell thickness about 1-2 μm).

FIG. 23(B) shows a light transmissivity characteristic with respect toan applied voltage for the thresholdless antiferroelectric mixed liquidcrystal exhibiting a V-shaped electrooptic response. The ordinate of thegraph of FIG. 23(B) represents a transmissivity (in an arbitrary unit)and the abscissa represents an applied voltage. The transmission axis ofa polarizing plate on the light receiving side of the liquid crystaldisplay is set almost parallel to a direction normal to the smecticlayer of the thresholdless antiferroelectric mixed liquid crystal, thedirection being almost aligned with the rubbing direction of the liquidcrystal display. The transmission axis of a polarizing plate on thelight projecting side is set almost at right angles to the transmissionaxis of the polarizing plate on the light receiving side (crossed-Nicolsarrangement).

FIG. 23(B) shows that the use of such a thresholdless antiferroelectricmixed liquid crystal enables a low voltage driving and a gray scaledisplay.

When the thresholdless antiferroelectric mixed liquid crystal with a lowvoltage driving is used on a liquid crystal display having an analogdriver, the power supply voltage for the video signal sampling circuitcan be suppressed to, for example, 5-8 V. Hence, the operation voltageof the driver can be lowered, realizing a reduction in power consumptionof the liquid crystal display and enhancing the reliability of thedisplay.

When the thresholdless antiferroelectric mixed liquid crystal with a lowvoltage driving is used on a liquid crystal display having a digitaldriver, the output voltage of a D/A converter circuit can be reduced.This enables the operation voltage of the D/A converter circuit to belowered, which in turn allows the operation voltage of the driver to bereduced, thus realizing reduced power consumption and enhancedreliability of the liquid crystal display.

Therefore, the thresholdless antiferroelectric mixed liquid crystal witha low voltage driving can also be effectively used when the TFTs with arelatively small width of LDD regions (low concentration impurityregions) (e.g., 0-500 nm or 0-200 nm) are used.

Generally, the thresholdless antiferroelectric mixed liquid crystalshave large spontaneous polarization and a high dielectric constant ofthe liquid crystal itself. Hence, when the thresholdlessantiferroelectric mixed liquid crystal is used on the liquid crystaldisplay, the pixels are required to have a relatively large storagecapacitor. Therefore, a thresholdless antiferroelectric mixed liquidcrystal with small spontaneous polarization should preferably be used.Further, it is possible to use a line-sequential driving method as thedriving method of the liquid crystal display and elongate the periodduring which to write a gray scale voltage into a pixel (pixel feedperiod) in order to compensate for a small storage capacitor.

The use of such a thresholdless antiferroelectric mixed liquid crystalrealizes a low voltage driving and therefore a low power consumption ofthe liquid crystal display.

In the field sequential driving method of this invention, one frame ofimage is divided into a plurality of subframes, i.e., the period of oneimage frame is divided into a plurality of subframe periods; red, greenand blue images are displayed during the corresponding subframe periods,respectively; and, when these color images are to be displayed, thecorresponding red, green and blue backlights are successively turned on.This arrangement can alleviate flicker of image experienced with theconventional display.

1. A liquid crystal display device comprising: a liquid crystal panelcomprising: a substrate; a pixel matrix circuit over the substrate,comprising a thin film transistor; and a backlight comprising a lightemitting diode, wherein a channel forming region of the thin filmtransistor comprising a polycrystalline silicon.
 2. A liquid crystaldisplay device comprising: a liquid crystal panel comprising: asubstrate; a drive circuit over the substrate; and a pixel matrixcircuit over the substrate, comprising a thin film transistor; and abacklight comprising a light emitting diode, wherein a channel formingregion of the thin film transistor comprising a polycrystalline silicon.3. A liquid crystal display device comprising: a liquid crystal panelcomprising: a substrate; a pixel matrix circuit over the substrate,comprising a thin film transistor; and an IC chip over the substrate;and a backlight comprising a light emitting diode, wherein a channelforming region of the thin film transistor comprising a polycrystallinesilicon.
 4. A liquid crystal display device comprising: a liquid crystalpanel comprising: a substrate; a drive circuit over the substrate; and apixel matrix circuit over the substrate, comprising a thin filmtransistor; and an IC chip over the substrate; and a backlightcomprising a light emitting diode, wherein a channel forming region ofthe thin film transistor comprising a polycrystalline silicon.
 5. Aliquid crystal display device comprising: a liquid crystal panelcomprising: a substrate; a pixel matrix circuit, comprising: a switchingthin film transistor over the substrate, having a first gate electrodeand a second gate electrode; a pixel electrode electrically connected tothe switching thin film transistor; and a gate line electricallyconnected to the first gate electrode and the second gate electrode; anda backlight comprising a light emitting diode, wherein a channel formingregion of the switching thin film transistor comprising apolycrystalline silicon.
 6. A liquid crystal display device comprising:a liquid crystal panel comprising: a substrate; a drive circuit over thesubstrate; a pixel matrix circuit, comprising: a switching thin filmtransistor over the substrate, having a first gate electrode and asecond gate electrode; a pixel electrode electrically connected to theswitching thin film transistor; and a gate line electrically connectedto the drive circuit, the first gate electrode and the second gateelectrode; and a backlight comprising a light emitting diode, wherein achannel forming region of the switching thin film transistor comprisinga polycrystalline silicon.
 7. A liquid crystal display devicecomprising: a liquid crystal panel comprising: a substrate; a pixelmatrix circuit, comprising: a switching thin film transistor over thesubstrate, having a first gate electrode and a second gate electrode; apixel electrode electrically connected to the switching thin filmtransistor; and a gate line electrically connected to the first gateelectrode and the second gate electrode; an IC chip over the substrate;and a backlight comprising a light emitting diode, wherein a channelforming region of the switching thin film transistor comprising apolycrystalline silicon.
 8. A liquid crystal display device comprising:a liquid crystal panel comprising: a substrate; a drive circuit over thesubstrate; a pixel matrix circuit, comprising: a switching thin filmtransistor over the substrate, having a first gate electrode and asecond gate electrode; a pixel electrode electrically connected to theswitching thin film transistor; and a gate line electrically connectedto the first gate electrode and the second gate electrode; an IC chipover the substrate; and a backlight comprising a light emitting diode,wherein a channel forming region of the switching thin film transistorcomprising a polycrystalline silicon.
 9. A liquid crystal display devicecomprising: a liquid crystal panel comprising: a substrate; and a pixelmatrix circuit over the substrate, comprising a thin film transistor;wherein a channel forming region of the thin film transistor comprisinga polycrystalline silicon, and wherein the liquid crystal display deviceis driven by a field sequential driving method.
 10. A liquid crystaldisplay device comprising: a liquid crystal panel comprising: asubstrate; a drive circuit over the substrate; and a pixel matrixcircuit over the substrate, comprising a thin film transistor; wherein achannel forming region of the thin film transistor comprising apolycrystalline silicon, and wherein the liquid crystal display deviceis driven by a field sequential driving method.
 11. A liquid crystaldisplay device comprising: a liquid crystal panel comprising: asubstrate; a pixel matrix circuit over the substrate, comprising a thinfilm transistor; and an IC chip over the substrate; wherein a channelforming region of the thin film transistor comprising a polycrystallinesilicon, and wherein the liquid crystal display device is driven by afield sequential driving method.
 12. A liquid crystal display devicecomprising: a liquid crystal panel comprising: a substrate; a drivecircuit over the substrate; and a pixel matrix circuit over thesubstrate, comprising a thin film transistor; and an IC chip over thesubstrate; wherein a channel forming region of the thin film transistorcomprising a polycrystalline silicon, and wherein the liquid crystaldisplay device is driven by a field sequential driving method.
 13. Aliquid crystal display device comprising: a liquid crystal panelcomprising: a substrate; a pixel matrix circuit, comprising: a switchingthin film transistor over the substrate, having a first gate electrodeand a second gate electrode; a pixel electrode electrically connected tothe switching thin film transistor; and a gate line electricallyconnected to the first gate electrode and the second gate electrode;wherein a channel forming region of the switching thin film transistorcomprising a polycrystalline silicon, and wherein the liquid crystaldisplay device is driven by a field sequential driving method.
 14. Aliquid crystal display device comprising: a liquid crystal panelcomprising: a substrate; a drive circuit over the substrate; and a pixelmatrix circuit, comprising: a switching thin film transistor over thesubstrate, having a first gate electrode and a second gate electrode; apixel electrode electrically connected to the switching thin filmtransistor; and a gate line electrically connected to the drive circuit,the first gate electrode and the second gate electrode; wherein achannel forming region of the switching thin film transistor comprisinga polycrystalline silicon, and wherein the liquid crystal display deviceis driven by a field sequential driving method.
 15. A liquid crystaldisplay device comprising: a liquid crystal panel comprising: asubstrate; a pixel matrix circuit, comprising: a switching thin filmtransistor over the substrate, having a first gate electrode and asecond gate electrode; a pixel electrode electrically connected to theswitching thin film transistor; and a gate line electrically connectedto the first gate electrode and the second gate electrode; and an ICchip over the substrate; wherein a channel forming region of theswitching thin film transistor comprising a polycrystalline silicon, andwherein the liquid crystal display device is driven by a fieldsequential driving method.
 16. A liquid crystal display devicecomprising: a liquid crystal panel comprising: a substrate; a drivecircuit over the substrate; a pixel matrix circuit, comprising: aswitching thin film transistor over the substrate, having a first gateelectrode and a second gate electrode; a pixel electrode electricallyconnected to the switching thin film transistor; and a gate lineelectrically connected to the drive circuit, the first gate electrodeand the second gate electrode; and an IC chip over the substrate;wherein a channel forming region of the switching thin film transistorcomprising a polycrystalline silicon, and wherein the liquid crystaldisplay device is driven by a field sequential driving method.
 17. Aliquid crystal display device comprising: a liquid crystal panelcomprising: a substrate; a pixel matrix circuit over the substrate,comprising a thin film transistor; and a backlight comprising a lightemitting diode, wherein a channel forming region of the thin filmtransistor comprising a polycrystalline silicon, and wherein the liquidcrystal display device is driven by a field sequential driving method.18. A liquid crystal display device comprising: a liquid crystal panelcomprising: a substrate; a drive circuit over the substrate; and a pixelmatrix circuit over the substrate, comprising a thin film transistor;and a backlight comprising a light emitting diode, wherein a channelforming region of the thin film transistor comprising a polycrystallinesilicon, and wherein the liquid crystal display device is driven by afield sequential driving method.
 19. A liquid crystal display devicecomprising: a liquid crystal panel comprising: a substrate; a pixelmatrix circuit over the substrate, comprising a thin film transistor;and an IC chip over the substrate; and a backlight comprising a lightemitting diode, wherein a channel forming region of the thin filmtransistor comprising a polycrystalline silicon, and wherein the liquidcrystal display device is driven by a field sequential driving method.20. A liquid crystal display device comprising: a liquid crystal panelcomprising: a substrate; a drive circuit over the substrate; and a pixelmatrix circuit over the substrate, comprising a thin film transistor;and an IC chip over the substrate; and a backlight comprising a lightemitting diode, wherein a channel forming region of the thin filmtransistor comprising a polycrystalline silicon, and wherein the liquidcrystal display device is driven by a field sequential driving method.21. A liquid crystal display device comprising: a liquid crystal panelcomprising: a substrate; a pixel matrix circuit, comprising: a switchingthin film transistor over the substrate, having a first gate electrodeand a second gate electrode; a pixel electrode electrically connected tothe switching thin film transistor; and a gate line electricallyconnected to the first gate electrode and the second gate electrode; anda backlight comprising a light emitting diode, wherein a channel formingregion of the switching thin film transistor comprising apolycrystalline silicon, and wherein the liquid crystal display deviceis driven by a field sequential driving method.
 22. A liquid crystaldisplay device comprising: a liquid crystal panel comprising: asubstrate; a drive circuit over the substrate; a pixel matrix circuit,comprising: a switching thin film transistor over the substrate, havinga first gate electrode and a second gate electrode; a pixel electrodeelectrically connected to the switching thin film transistor; and a gateline electrically connected to the drive circuit, the first gateelectrode and the second gate electrode; and a backlight comprising alight emitting diode, wherein a channel forming region of the switchingthin film transistor comprising a polycrystalline silicon, and whereinthe liquid crystal display device is driven by a field sequentialdriving method.
 23. A liquid crystal display device comprising: a liquidcrystal panel comprising: a substrate; a pixel matrix circuit,comprising: a switching thin film transistor over the substrate, havinga first gate electrode and a second gate electrode; a pixel electrodeelectrically connected to the switching thin film transistor; and a gateline electrically connected to the first gate electrode and the secondgate electrode; an IC chip over the substrate; and a backlightcomprising a light emitting diode, wherein a channel forming region ofthe switching thin film transistor comprising a polycrystalline silicon,and wherein the liquid crystal display device is driven by a fieldsequential driving method.
 24. A liquid crystal display devicecomprising: a liquid crystal panel comprising: a substrate; a drivecircuit over the substrate; a pixel matrix circuit, comprising: aswitching thin film transistor over the substrate, having a first gateelectrode and a second gate electrode; a pixel electrode electricallyconnected to the switching thin film transistor; and a gate lineelectrically connected to the drive circuit, the first gate electrodeand the second gate electrode; an IC chip over the substrate; and abacklight comprising a light emitting diode, wherein a channel formingregion of the switching thin film transistor comprising apolycrystalline silicon, and wherein the liquid crystal display deviceis driven by a field sequential driving method.
 25. A liquid crystaldevice according to claim 1, wherein the light emitting diode is any oneof a red light emitting diode, green light emitting diode and blue lightemitting diode.
 26. A liquid crystal device according to claim 2,wherein the light emitting diode is any one of a red light emittingdiode, green light emitting diode and blue light emitting diode.
 27. Aliquid crystal device according to claim 3, wherein the light emittingdiode is any one of a red light emitting diode, green light emittingdiode and blue light emitting diode.
 28. A liquid crystal deviceaccording to claim 4, wherein the light emitting diode is any one of ared light emitting diode, green light emitting diode and blue lightemitting diode.
 29. A liquid crystal device according to claim 5,wherein the light emitting diode is any one of a red light emittingdiode, green light emitting diode and blue light emitting diode.
 30. Aliquid crystal device according to claim 6, wherein the light emittingdiode is any one of a red light emitting diode, green light emittingdiode and blue light emitting diode.
 31. A liquid crystal deviceaccording to claim 7, wherein the light emitting diode is any one of ared light emitting diode, green light emitting diode and blue lightemitting diode.
 32. A liquid crystal device according to claim 8,wherein the light emitting diode is any one of a red light emittingdiode, green light emitting diode and blue light emitting diode.
 33. Aliquid crystal device according to claim 17, wherein the light emittingdiode is any one of a red light emitting diode, green light emittingdiode and blue light emitting diode.
 34. A liquid crystal deviceaccording to claim 18, wherein the light emitting diode is any one of ared light emitting diode, green light emitting diode and blue lightemitting diode.
 35. A liquid crystal device according to claim 19,wherein the light emitting diode is any one of a red light emittingdiode, green light emitting diode and blue light emitting diode.
 36. Aliquid crystal device according to claim 20, wherein the light emittingdiode is any one of a red light emitting diode, green light emittingdiode and blue light emitting diode.
 37. A liquid crystal deviceaccording to claim 21, wherein the light emitting diode is any one of ared light emitting diode, green light emitting diode and blue lightemitting diode.
 38. A liquid crystal device according to claim 22,wherein the light emitting diode is any one of a red light emittingdiode, green light emitting diode and blue light emitting diode.
 39. Aliquid crystal device according to claim 23, wherein the light emittingdiode is any one of a red light emitting diode, green light emittingdiode and blue light emitting diode.
 40. A liquid crystal deviceaccording to claim 24, wherein the light emitting diode is any one of ared light emitting diode, green light emitting diode and blue lightemitting diode.
 41. A liquid crystal display device according to claim5, the switching thin film transistor comprising a semiconductor layerover the substrate, having a first doped region and a second dopedregion, wherein the consistency of the first doped region is lower thanthe second doped region.
 42. A liquid crystal display device accordingto claim 6, the switching thin film transistor comprising asemiconductor layer over the substrate, having a first doped region anda second doped region, wherein the consistency of the first doped regionis lower than the second doped region.
 43. A liquid crystal displaydevice according to claim 7, the switching thin film transistorcomprising a semiconductor layer over the substrate, having a firstdoped region and a second doped region, wherein the consistency of thefirst doped region is lower than the second doped region.
 44. A liquidcrystal display device according to claim 8, the switching thin filmtransistor comprising a semiconductor layer over the substrate, having afirst doped region and a second doped region, wherein the consistency ofthe first doped region is lower than the second doped region.
 45. Aliquid crystal display device according to claim 13, the switching thinfilm transistor comprising a semiconductor layer over the substrate,having a first doped region and a second doped region, wherein theconsistency of the first doped region is lower than the second dopedregion.
 46. A liquid crystal display device according to claim 14, theswitching thin film transistor comprising a semiconductor layer over thesubstrate, having a first doped region and a second doped region,wherein the consistency of the first doped region is lower than thesecond doped region.
 47. A liquid crystal display device according toclaim 15, the switching thin film transistor comprising a semiconductorlayer over the substrate, having a first doped region and a second dopedregion, wherein the consistency of the first doped region is lower thanthe second doped region.
 48. A liquid crystal display device accordingto claim 16, the switching thin film transistor comprising asemiconductor layer over the substrate, having a first doped region anda second doped region, wherein the consistency of the first doped regionis lower than the second doped region.
 49. A liquid crystal displaydevice according to claim 21, the switching thin film transistorcomprising a semiconductor layer over the substrate, having a firstdoped region and a second doped region, wherein the consistency of thefirst doped region is lower than the second doped region.
 50. A liquidcrystal display device according to claim 22, the switching thin filmtransistor comprising a semiconductor layer over the substrate, having afirst doped region and a second doped region, wherein the consistency ofthe first doped region is lower than the second doped region.
 51. Aliquid crystal display device according to claim 23, the switching thinfilm transistor comprising a semiconductor layer over the substrate,having a first doped region and a second doped region, wherein theconsistency of the first doped region is lower than the second dopedregion.
 52. A liquid crystal display device according to claim 24, theswitching thin film transistor comprising a semiconductor layer over thesubstrate, having a first doped region and a second doped region,wherein the consistency of the first doped region is lower than thesecond doped region.
 53. An electronic device comprising the liquidcrystal display device according to claim 1, wherein the electronicdevice is selected from the group consisting of digital a camera, a carnavigation system, a personal computer, a mobile information terminal, acellular phone.
 54. An electronic device comprising the liquid crystaldisplay device according to claim 2, wherein the electronic device isselected from the group consisting of digital a camera, a car navigationsystem, a personal computer, a mobile information terminal, a cellularphone.
 55. An electronic device comprising the liquid crystal displaydevice according to claim 3, wherein the electronic device is selectedfrom the group consisting of digital a camera, a car navigation system,a personal computer, a mobile information terminal, a cellular phone.56. An electronic device comprising the liquid crystal display deviceaccording to claim 4, wherein the electronic device is selected from thegroup consisting of digital a camera, a car navigation system, apersonal computer, a mobile information terminal, a cellular phone. 57.An electronic device comprising the liquid crystal display deviceaccording to claim 5, wherein the electronic device is selected from thegroup consisting of digital a camera, a car navigation system, apersonal computer, a mobile information terminal, a cellular phone. 58.An electronic device comprising the liquid crystal display deviceaccording to claim 6, wherein the electronic device is selected from thegroup consisting of digital a camera, a car navigation system, apersonal computer, a mobile information terminal, a cellular phone. 59.An electronic device comprising the liquid crystal display deviceaccording to claim 7, wherein the electronic device is selected from thegroup consisting of digital a camera, a car navigation system, apersonal computer, a mobile information terminal, a cellular phone. 60.An electronic device comprising the liquid crystal display deviceaccording to claim 8, wherein the electronic device is selected from thegroup consisting of digital a camera, a car navigation system, apersonal computer, a mobile information terminal, a cellular phone. 61.An electronic device comprising the liquid crystal display deviceaccording to claim 9, wherein the electronic device is selected from thegroup consisting of digital a camera, a car navigation system, apersonal computer, a mobile information terminal, a cellular phone. 62.An electronic device comprising the liquid crystal display deviceaccording to claim 10, wherein the electronic device is selected fromthe group consisting of digital a camera, a car navigation system, apersonal computer, a mobile information terminal, a cellular phone. 63.An electronic device comprising the liquid crystal display deviceaccording to claim 11, wherein the electronic device is selected fromthe group consisting of digital a camera, a car navigation system, apersonal computer, a mobile information terminal, a cellular phone. 64.An electronic device comprising the liquid crystal display deviceaccording to claim 12, wherein the electronic device is selected fromthe group consisting of digital a camera, a car navigation system, apersonal computer, a mobile information terminal, a cellular phone. 65.An electronic device comprising the liquid crystal display deviceaccording to claim 13, wherein the electronic device is selected fromthe group consisting of digital a camera, a car navigation system, apersonal computer, a mobile information terminal, a cellular phone. 66.An electronic device comprising the liquid crystal display deviceaccording to claim 14, wherein the electronic device is selected fromthe group consisting of digital a camera, a car navigation system, apersonal computer, a mobile information terminal, a cellular phone. 67.An electronic device comprising the liquid crystal display deviceaccording to claim 15, wherein the electronic device is selected fromthe group consisting of digital a camera, a car navigation system, apersonal computer, a mobile information terminal, a cellular phone. 68.An electronic device comprising the liquid crystal display deviceaccording to claim 16, wherein the electronic device is selected fromthe group consisting of digital a camera, a car navigation system, apersonal computer, a mobile information terminal, a cellular phone. 69.An electronic device comprising the liquid crystal display deviceaccording to claim 17, wherein the electronic device is selected fromthe group consisting of digital a camera, a car navigation system, apersonal computer, a mobile information terminal, a cellular phone. 70.An electronic device comprising the liquid crystal display deviceaccording to claim 18, wherein the electronic device is selected fromthe group consisting of digital a camera, a car navigation system, apersonal computer, a mobile information terminal, a cellular phone. 71.An electronic device comprising the liquid crystal display deviceaccording to claim 19, wherein the electronic device is selected fromthe group consisting of digital a camera, a car navigation system, apersonal computer, a mobile information terminal, a cellular phone. 72.An electronic device comprising the liquid crystal display deviceaccording to claim 20, wherein the electronic device is selected fromthe group consisting of digital a camera, a car navigation system, apersonal computer, a mobile information terminal, a cellular phone. 73.An electronic device comprising the liquid crystal display deviceaccording to claim 21, wherein the electronic device is selected fromthe group consisting of digital a camera, a car navigation system, apersonal computer, a mobile information terminal, a cellular phone. 74.An electronic device comprising the liquid crystal display deviceaccording to claim 22, wherein the electronic device is selected fromthe group consisting of digital a camera, a car navigation system, apersonal computer, a mobile information terminal, a cellular phone. 75.An electronic device comprising the liquid crystal display deviceaccording to claim 23, wherein the electronic device is selected fromthe group consisting of digital a camera, a car navigation system, apersonal computer, a mobile information terminal, a cellular phone. 76.An electronic device comprising the liquid crystal display deviceaccording to claim 24, wherein the electronic device is selected fromthe group consisting of digital a camera, a car navigation system, apersonal computer, a mobile information terminal, a cellular phone.